I'm using Foundation 5 with a slight adjustment (page width = 80em, breakpoint still 58,75em). However, when I reduce the viewport, the won't adjust to the mobile version (dropdown menu button) until the viewport is less than 645px wide. It should adjust itself when viewport is less than 940px.

How do I configure that?

I haven't done any adjustments, not JS nor CSS, so It's (probably) not my fault for that behaviour.

I'm using Foundation 5 with a slight adjustment (page width = 80em, breakpoint still 58,75em). However, when I reduce the viewport, the won't adjust to the mobile version (dropdown menu button) until the viewport is less than 645px wide. It should adjust itself when viewport is less than 940px.

How do I configure that?

I haven't done any adjustments, not JS nor CSS, so It's (probably) not my fault for that behaviour.

Just wondering can this value be changed using CSS only? I have changed the visual elements in the CSS to a wider breakpoint and this works fine but the Javascript doesn't kick in until the default setting (approx 640px).

From what I understand from the original post the issue you are having is the javascript - therefore for the mobile dropdown menu isn't firing until you get down to 640px - I was having the same issue - had been tinkering with the CSS and Topbar.js trying to figure out what was doing what and stumbled across a solution that works in my case - why it works I don't know but it might prove useful...

First I duplicated the meta.foundation-mq-topbar class (foundation.css) and all its properties and renamed it .topbar-breakpoint then changed the values to the breakpoint I required (in this case 60em) so that I ended up with:

The styles are doing what I want them to do, but the Javascript isn't activated when I click the toggle-top-bar menu-icon unless it is within the 40.063em range. Looking in the firebug console the class 'expanded' isn't being added so this is why I think something is either wrong with the javascript

@jason
I had to change the following (foundation 5.4.7 css version) to change the breakpoint

1) Search for "meta.foundation-mq-topbar" (~ line 1741) and modify both widths. It appears information is being passed in the font family, when I did NOT change that value, javascript did not kick in"
2) Search for "@media only screen and (min-width: 40.063em) { .top-bar {" (~ line 2062) and change value there
3) Search for "@media only screen and (max-width: 40em) { .top-bar" (~line 1796) and change value there.